Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [patch,v2] bdi: add a user-tunable cpu_list for the bdi flusher threads | Date | Tue, 04 Dec 2012 17:26:26 -0500 |
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Jens Axboe <jaxboe@fusionio.com> writes:
>>>> @@ -437,6 +488,14 @@ static int bdi_forker_thread(void *ptr) >>>> spin_lock_bh(&bdi->wb_lock); >>>> bdi->wb.task = task; >>>> spin_unlock_bh(&bdi->wb_lock); >>>> + mutex_lock(&bdi->flusher_cpumask_mutex); >>>> + ret = set_cpus_allowed_ptr(task, >>>> + bdi->flusher_cpumask); >>>> + mutex_unlock(&bdi->flusher_cpumask_mutex); >>> >>> It'd be very useful if we had a kthread_create_cpu_on_cpumask() instead >>> of a _node() variant, since the latter could easily be implemented on >>> top of the former. But not really a show stopper for the patch... >> >> Hmm, if it isn't too scary, I might give this a try. > > Should not be, pretty much just removing the node part of the create > struct passed in and making it a cpumask. And for the on_node() case, > cpumask_of_ndoe() will do the trick.
I think it's a bit more involved than that. If you look at kthread_create_on_node, the node portion only applies to where the memory comes from, it says nothing of scheduling. To whit:
/* * root may have changed our (kthreadd's) priority or CPU mask. * The kernel thread should not inherit these properties. */ sched_setscheduler_nocheck(create.result, SCHED_NORMAL, ¶m); set_cpus_allowed_ptr(create.result, cpu_all_mask);
So, if I were to make the change you suggested, I would be modifying the existing behaviour. The way things stand, I think kthread_create_on_node violates the principal of least surprise. ;-) I would prefer a variant that affected scheduling behaviour as well as memory placement. Tejun, Peter, Ingo, what are your opinions?
Cheers, Jeff
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